This invention relates to a lamp lighting controlling apparatus and light emitting apparatus used for an exposure apparatus for exposing a substrate such as a display board, print circuit board, semiconductor wafer etc., especially, to a lamp lighting controlling apparatus and a light emitting apparatus for precisely controlling desired accumulated light amount on a work piece or work pieces suitable for sputtering etc.
In such an exposure apparatus for exposing a substrate or substrates such as a display board, a print circuit board, a semiconductor wafer etc., a light emitting apparatus for emitting exposure light is provided.
In FIG. 8, the structure of such the light emitting apparatus 10 is shown.
As shown in the figure, in a light emitting unit 10, optical components such as a discharge lamp 1, e.g. an ultrahigh-pressure mercury lamp, that emits exposure light, a condensing mirror 2 for condensing light from the discharge lamp 1, a first plane mirror 4 (a reflecting mirror) for reflecting the light from the discharge lamp 1 and the condensing mirror 2, an integrator lens 5 for making the illumination distribution uniform on a light exposure surface, a second plane mirror 7 (a reflecting mirror) for conducting light to a light outgoing window, and a collimator lens 8 for forming light emitted from the light outgoing window into parallel light.
A shutter mechanism 6 comprises a shutter plate 61 (a douser), a shutter driving unit 62, and a shutter opening/closing detecting sensor 63.
The shutter plate 61 is driven by the shutter driving unit 62, and the light emitting amount (light exposure amount) emitted on the light exposure surface is controlled by inserting the shutter plate 61 in the optical path or removing the plate 61 from the optical path.
A open/close state of the shutter 61 is detected by the shutter opening/closing detecting sensor 63. The light exposure surface may be a mask surface on which a pattern of circuit etc. is formed or a work surface on which a photosensitive agent is coated and formed.
An illuminometer 11 provided behind the second plane mirror 7, receives light through a light transmission portion such as a pinhole(s) provided on the second plane mirror 7. Output of the illuminometer 11 is sent to an accumulated light amount measuring unit 12.
In the accumulated light amount measuring unit 12, accumulated light amount is calculated by accumulating light amount measured by the illuminometer 11.
The lamp lighting controlling apparatus 20 comprises a lamp lighting power source 21 for supplying power to turn on the lamp 1, and a controlling unit 22.
The lamp lighting power source 21 has a power supply unit 21a and a start-up circuit 21b (a starter). The power supply unit 21a converts AC into DC and supplies it to the lamp 1. Power supplied to the lamp 1 is controlled by the lamp lighting power source 21.
The start-up circuit 21b generates high voltage so that dielectric breakdown takes place between electrodes of the lamp 1 at the start of discharge lamp lighting.
In turning on a short-arc discharge lamp such as an ultrahigh-pressure mercury discharge lamp, high voltage is instantaneously impressed between the electrodes at a frequency greater than 1 MHz so that the dielectric breakdown takes place and the discharge lamp is turned on. The start-up circuit is called an ignitor, or a starter.
The controlling unit 22 receives output of a controlling section 23 for controlling the exposure apparatus, and controls opening of the shutter plate 61 according to output from the controlling section 23, the accumulated light amount measuring unit 12 and the shutter opening/closing detecting sensor 63 or controls to turn on and off the lamp 1 by controlling the lamp lighting power source 21.
In the light emitting unit 10, the lamp 1 is always tuned on.
In order to make the accumulated light amount emitted on the work piece having the light exposure surface uniform, the controller 22 controls opening of the shutter plate 61 during a period from the opening of the shutter (the start of emission) to the closing of the shutter (end of emission) by controlling the shutter mechanism 6 according to the output of the accumulated light amount measuring unit 12 so that accumulated light amount (light exposure amount) on the light exposure surface becomes a desired value.
The lamp 1 is always turned on because in general once the lamp 1 including mercury in inclusive gas is turned off, the lamp 1 cannot be re-lighted easily since the dielectric breakdown voltage is high while the temperature of the lamp is still high, therefore, the lamp 1 would not be tuned on unless the lamp is cooled off so that the dielectric breakdown voltage becomes sufficiently low.
xe2x80x9cRelightxe2x80x9d means that power is applied to the lamp 1 to turn on the lamp after the lamp is turned off but while the lamp does not sufficiently cool down.
In FIGS. 9A and 9B, an example of the shutter mechanism 6 for the light emitting apparatus is shown.
The shutter plate 61 has light transmission portions 64 and light blocking portions 65. The shutter plates 61 are unidirectionally (in a direction shown as an arrow) rotated with respect to a rotation axis 66 by the shutter driving unit 62 such as a motor (not shown).
When the shutter plate 61 is in a position shown in FIG. 9A, light passes through the light transmission portion 64. When the shutter plate 61 is in a position shown in FIG. 9B, the light is blocked by the light blocking portions 65.
Description of the conventional accumulated light exposure amount control in the light emitting apparatus shown in FIG. 8 will be given below.
At the beginning, the lamp 1 is turned on. When the lighting becomes stable and a work piece such as a wafer etc. is placed on the light exposure surface, the controlling unit 22 sends a shutter opening command to the shutter driving unit 62. And then the shutter plate 61 is opened and light is emitted from the light outgoing window and then the wafer etc. placed on the light exposure surface is exposed.
The accumulated light exposure amount on the light exposure surface is controlled as described below.
As shown in FIG. 8, the illuminometer 11 is provided behind the second plane mirror 7, and light transmitted through the light transmission portion such as a pinhole(s) etc. provided on part of the second plane mirror 7 is entered into the illuminometer 11.
The illuminometer 11 is not placed on the light exposure surface since the shadow of the illuminometer 11 appears against the work piece (a mask etc.) during an actual exposure operation if the illuminometer 11 is placed on the light exposure surface and it is impossible to measure the illumination intensity.
In case that the illuminometer 11 receives the light transmitted through the light transmission portion, it is necessary to be set so that accumulated light amount exposed on the light exposure surface and accumulated light amount measured from the amount of light received by the illuminometer 11 are equivalent.
In particular, it is confirmed that they are in proportionality relation, and the constant of proportion is obtained.
An illumination intensity signal from the illuminometer 11 is input in the accumulated light amount measuring unit 12 and converted into accumulated light exposure amount.
The controlling unit 22 sends a shutter closing command to the shutter driving unit 62 so that the accumulated light amount is controlled to a predetermined value by predictive control described below and closes the shutter plate 61. The operation constitutes one cycle of exposure process for the wafer etc.
As shown in FIGS. 9A and 9B, the shutter plate 61 is rotated. Therefore, it takes minimum amount of time to completely block light trace from a time when the shutter opening command is input to a time when the shutter plate 61 is completely opened and complete light passes through the light transmission portion, or from a time when the shutter closing command is input to a time when the shutter plate is completely closed.
The operation period of the shutter is about 20 ms even though driving mechanism capable of operating at high speed is used.
In FIG. 10, change of illumination intensity (that is, intensity change of a light signal from the illuminometer 11) from a time when the shutter is opened to a time when the shutter is closed is shown.
In the figure, a section marked with diagonal lines shows accumulated light exposure amount. The curved line showing illumination intensity is waved because of flicker (ripple) of light emitted from the lamp 1. This ripple causes subtle change of illumination intensity on the light exposure surface.
The light exposure amount in a period during which the shutter is in operation (a period from the beginning of shutter opening operation to the completion of the opening operation), is shown as a right side triangle portion B.
The accumulated light exposure amount marked with the diagonal lines in FIG. 10 is controlled to a desired light exposure amount by controlling the opening and closing of the shutter. Description of the control is given below.
Illumination intensity is measured by the illuminometer 11 from a time when the shutter command signal is sent to the shutter driving unit 62 (the start of a shutter opening operation), and light amount is accumulated in the accumulated light amount measuring unit 12 and the accumulated light amount is calculated.
However, if a shutter closing operation starts when the light exposure reaches a desired value, excessive light amount is exposed since the right triangle portion B shown FIG. 10 is added to the accumulated light amount.
Therefore, in the controlling unit 22, the light amount A during the shutter opening operation is stored based on output of the accumulated light amount measuring unit 12.
Assuming that the light exposure amount A in the shutter opening operation and the light exposure amount B in the shutter closing operation are equal (A=B), the accumulated light exposure amount reaches a value less than a desired value by the light exposure amount A, the controlling unit 22 sends a shutter closing command to the shutter driving unit, the shutter plate 61 starts a closing operation.
That is, based on the assumption of A=B, the predictive control is carried out. The calculation of light exposure amount in the shutter opening operation is performed every exposure.
Thus, the light exposure amount is controlled based on the prediction that the light exposure amount A during the shutter opening operation and the light exposure amount B during the shutter closing operation are equal.
To satisfy the requirement of A=B, the shutter opening speed and the shutter closing speed must be equal and also ripple of light must be equal.
It is difficult to completely eliminate the ripple and it is impossible to control the size or frequency of the ripple. Therefore, the light exposure amount A and the light exposure amount B are subtly different because of changes of the ripple (that is subtle changes of the illumination intensity).
Also, it is difficult to completely eliminate fluctuation in a shutter mechanism driving operation, e.g. fluctuation of a period from input of the shutter opening command or input of the shutter closing command in the shutter mechanism 6, to the start of the shutter opening or closing operation. In FIG. 10, the fluctuation is shown as a portion marked with diagonal dash lines.
More precisely, when the operation period of the shutter is 20 ms, there is an error of about xc2x10.2 ms. This will cause a light exposure amount error of xc2x11% or more during the shutter closing operation. Therefore, it is difficult to control such light exposure amount error to less than xc2x11% and there is about 0.5% of fluctuation in the light exposure amount as a whole.
In recent years, it is increasingly necessary to precisely control the light exposure amount in order to carry out light exposure with miniaturization and high precision which is suitable for network operations.
Specifically, in the recent years, high-sensitivity of photosensitive material (resist) for light exposure has been advanced in order to carry out light exposure for a short time with a small amount of light exposure.
Conventionally, in the light exposure control, 2% of error was permissible, however, it is desired to control the error to less than 1%, preferably, less than 0.5%.
It is an object of the present invention to precisely control light exposure amount in carrying out light exposure on a substrate such as a semiconductor wafer.
It is another object of the present invention to minimize fluctuation of the light exposure amount due to ripple of light from the lamp and fluctuation of an operation of shutter mechanism.
In the conventional light emitting apparatus as described above, the lamp is always turned on. This is why in general once the discharge lamp including mercury in enclosed gas is turned off, the lamp will not be relighted immediately, since dielectric breakdown voltage is high while the lamp is still hot.
However, in an actual experiment for relighting such an ultrahigh-pressure mercury lamp, it was found that the lamp can be relighted within a limited time.
In FIG. 11, an experiment result of relightable time in the experiment in which a 4 W ultrahigh-pressure mercury lamp is used is shown.
As understood from the figure, it is possible to relight the lamp within 4 seconds after the lamp is turned off.
This is one of examples but any discharge lamp may be relighted if it is relighted within a short time.
It is presumed that the dielectric breakdown voltage is still low, if vapor of mercury generated in the lamp case when the lamp is tuned on does not disappear, that is, the vapor remains for a while after the lamp is turned off.
On the other hand, if the lamp is tuned off in such manner described above, the lamp must be relighted within the period during which the relighting is possible.
Also high voltage must be impressed to the lamp from the starter (start-up circuit).
However, if lighting to reduce power is maintained, the restriction that the lamp must be relighted within the time during which the lamp can be relighted is removed. Further, since it is not necessary to impress high voltage to the lamp from the starter (start-up circuit), design freedom is increased as to light exposure processing control in the apparatus.
The present invention solves the problems as set forth below.
Using the characteristic of a discharge lamp, accumulated light exposure amount is controlled to a desired value by turning off the lamp for a short time when the accumulated light exposure amount reaches a desired amount and the shutter is closed during the short period.
That is, during a period of the discharge lamp""s lighting, a shutter opening command is output to the shutter driving mechanism 6, and light is exposed on the light exposure surface. When the accumulated light amount measured by the accumulated light amount measuring unit reaches a predetermined value, a lamp OFF signal is output to the lamp lighting power source 21, and light emission on the light exposure surface is stopped, and, at the same time, a shutter closing command is output to the shutter mechanism 6 and then a lamp relighting command is output to the lamp lighting power source after the shutter is closed and within the period during which relighting of the discharge lamp is possible.
Thus, within the turning off period during which relighting of the discharge lamp is possible, the closing of the shutter plate 61 is completed and relighting is carried out.
In other words, the lamp turning off period is at least longer than a shutter closing period and shorter than the period during which relighting is possible.
Thus, it is possible to precisely control the light exposure amount without effects of ripple of light from the discharge lamp and/or fluctuation of a shutter mechanism driving operation.
The present invention also solves the problems as set forth below.
When the shutter closing operation takes place, illumination intensity on the light exposure surface is reduced by decreasing power supplied to the lamp to less than the rated apparent power. After the shutter closing operation is completed, the power supplied to the lamp is set back to the rated apparent power before the discharge lamp is turned off.
For example, if the power supplied to the lamp 1 is reduced to 1/n, the illumination intensity is proportional to it and reduced to 1/n.
A predictive control in which (1/n)xc3x97A=B is assumed is carried out.
That is, during lighting of the discharge lamp 1, a shutter opening command is output to the shutter mechanism 6 and light is emitted onto the light exposure surface.
Assuming that 1/n of exposure amount A during the period of the shutter opening operation and the exposure amount B during the shutter closing operation are equal [(1/n)xc3x97A=B], when the accumulated light exposure amount, measured by the accumulated light amount measuring unit 12, from the start of the shutter opening operation, reaches a certain light exposure amount which is less than the predetermined exposure amount by (1/n)xc3x97A, a command for reducing power supplied to the discharge lamp 1 is sent to the lamp lighting power source 21 so that intensity of light emission on the light exposure surface is decreased. At the same time, a shutter closing command is sent to the shutter mechanism 6.
After the shutter closing operation is completed, power supplied to the discharge lamp 1 is increased to the rated apparent power before the lamp 1 is turned off.
The value xe2x80x9cnxe2x80x9d of [1/n rated apparent power] is set not to turn off the lamp 1 during the shutter closing operation. For example, preferably, 1/n equals to about 0.1-0.3.
Since the lower the power supplied to the lamp 1 is with the value xe2x80x9cnxe2x80x9d increased, the less the error of the light exposure amount is, if n=10, it is possible to make the error of the light exposure amount the least.
Since the light exposure amount is small during the shutter closing operation since the intensity of light emission onto the light exposure surface during the shutter closing operation is low, it is possible to output the shutter closing command when the accumulated light exposure amount measured by the accumulated light exposure measuring unit 12, reaches a predetermined light exposure amount without the prediction control described above if such light exposure amount does not become problematic.
As described above, if the illumination intensity is set to 1/n in the shutter closing operation, the error of the light exposure amount generated in the portion B described above becomes 1/n of the conventional error. Therefore, the 2% of the error in the conventional apparatus becomes 2/n % in the present invention.
When the lamp 1 is turned off as in the first method described at above, it is possible to eliminate the errors of light exposure amount, but the lamp 1 must be relighted within the period during which relighting is possible.
As in the second method, when the power supplied to the lamp 1 is lowered and the lighting is maintained, the restriction that the lamp 1 must be relighted within the period during which relighting is possible is eliminated and freedom of design as to the exposure processing control of the apparatus is increased.
Also it is not necessary to relight the lamp 1 by impressing high voltage to the lamp 1 by the starter (start-up circuit).